1. Field of the Invention
The present invention pertains to a large bore float assembly. More particularly, the present invention pertains to a large bore float assembly having at least one flapper valve. More particularly still, the present invention pertains to a float assembly having non-metallic valves and other components, yet providing a greater pressure rating than conventional float assemblies.
2. Brief Description of the Prior Art
Drilling of an oil or gas well is frequently accomplished using a surface drilling rig and tubular drill pipe. When installing drill pipe (or other tubular goods) into a well, such pipe is typically inserted into a wellbore in a number of sections of roughly equal length called “joints”. As the pipe penetrates deeper into a well, additional joints of pipe must be added to the ever lengthening “drill string” at the drilling rig. As such, a typical drill string comprises a plurality of sections or joints of pipe, each of which has an internal, longitudinally extending bore.
After a well is drilled to a desired depth, relatively large diameter pipe known as casing is typically installed and cemented in place within the wellbore. Cementing is performed by pumping a predetermined volume of cement slurry into the well using high-pressure pumps. The cement slurry is typically pumped down the inner bore of the casing, out the distal end of the casing, and back up around the outer surface of the casing. After the predetermined volume of cement is pumped, a plug or wiper assembly is typically pumped down the inner bore of the casing using drilling mud or other fluid in order to fully displace the cement from the inner bore of the casing. In this manner, the cement slurry leaves the inner bore of the casing and enters the annular space existing between the outer surface of the casing and the inner surface of the wellbore. As such cement hardens, it should beneficially secure the casing in place and form a seal to prevent fluid flow along the outer surface of the casing.
In many conventional cementing operations, an apparatus known as a float collar or float assembly is frequently utilized at or near the bottom (distal) end of the casing string. In most cases, the float assembly comprises a short length of casing or other tubular housing fitted with a check valve assembly, such as a flapper-valve, spring-loaded ball valve or other type of closing mechanism. The check-valve assembly permits the cement slurry to flow out the distal end of the casing, but prevents back-flow of the heavier cement slurry into the inner bore of the casing when pumping stops. Without such a float collar, the heavy cement slurry pumped into the annular space around the outside of the casing can U-tube or reverse flow back into the inner bore of the casing, which can result in a very undesirable situation.
Auto-fill float systems comprise specialized float collar assemblies that have been long known and widely used in the oil and gas industry. Generally, auto-fill float systems consist of float assemblies with one or more flapper-style valves run into a wellbore in an open position, such that wellbore fluids can flow bi-directionally through the assembly. When desired, said valves can be selectively closed via actuation mechanism(s); such activation mechanisms can include, for example, pressure and/or flow rate increases through the casing string. One common actuation mechanism involves insertion of a tubular member or sleeve through the valve body(ies) in order to hold the flapper(s) open. When desired, the tubular member can be selectively expelled from the assembly via a drop ball or other item; with the sleeve out of the way, the valve(s) are permitted to close.
As with virtually any float assembly, after cement slurry has been pumped and set, the float assembly must frequently be drilled out, typically with a PDC or roller-cone type bit. As such, the need for constructing float collar assemblies from drillable materials—such as composite material—is paramount. While composite valve bodies and flappers have existed for some time, both ferrous and non-ferrous metallic components continue to be used in the form of shear pins, hinge pins, and valve springs. Additionally, existing auto-fill systems have limited to no capability to adjust the activation variables such as, for example, deactivation pressure and/or flow rate. Such considerations highlight the need for improvement over existing prior art float assemblies.
Further, although float assemblies have been known in the art for some time, many have relatively small internal flow bores. As a result, pieces of rock or debris including, without limitation, debris suspended within the cement slurry can become lodged in the inner bore of the float assembly, thereby impeding progress of cementing operations and creating an unsafe condition. Further, problems exist with many existing prior art float valve assemblies, in terms of both actuation and the ability to withstand pressure loading.
Thus, there is a need for a durable, easily drillable, large-bore float assembly having at least one reliable, high-pressure valve assembly that can withstand significant wellbore pressures.